Research Of Heat Transfer Performance On Composite Added MPCMs

The composite phase change material prepared by method of microcapsule has become a research focus in energy utilization and material science with the rapid development of micro/nano technology and polymer technology. The complex working medium contains phase change microcapsules uses dielectric materials for realizing heat transfer enhancement of the phase change material. The work can form a kind of composite phase change material of great use value and development prospects. The composite material has spatial structure and complex heat transfer process. It blocks the establishment of scientific and effective characterization method. And this is one of the bottlenecks to restrict research and development of the materials. In the paper, the methods of theoretical analysis and numerical simulation are combined. The scientific characterization method of the heat transfer performance and characteristic in the complex working medium are investigated.Two-Temperature Model which can reflect the heat exchange between dielectric materials and phase change material is established from the structure characteristics of the microencapsulated phase change material suspension. The main characteristics:(1) The relative motion between dielectric materials and phase change material is ignored.(2) Assume that the heat only transferred in the dielectric materials system and the heat diffusion in the phase change material system is ignored.(3) The heat transfer between dielectric materials and phase change material is simplified as a linear function of the temperature difference between them at the same point in space and time. This model can be used in the finalized composite material contains phase change microcapsules when the velocity is zero. Then it can become the general heat transfer model of complex working medium contains phase change microcapsules. In this paper, the physical meaning of the heat transfer characteristic parameters in the Two-Temperature Model is analyzed. And the model is compared and analyzed with the equivalent specific heat model and the two-fluid model at the same time.The paper takes the heat transfer process of the phase change energy storage plasterboard as a example, the one-dimensional unsteady form of the energy equation of this model is numerically solved by finite difference method. According to the simulated results, the distribution law of the temperature difference between dielectric materials system and phase change material system of time and space is analyzed under the first type boundary condition. Meanwhile, the effect of the volume concentration of phase change microcapsules and the unit thermal resistance between dielectric materials system and phase change material system in the plasterboard on the attenuation and delay of temperature wave is analyzed under the third type boundary condition of the periodic environment temperature. The convective heat transfer of the microencapsulated phase change material suspension do laminar flow in a circular tube is used as an example. Then the effect of some heat transfer characteristic parameters such as the volume concentration of phase change microcapsules and the unit thermal resistance between dielectric materials system and phase change material system on some parameters like convective heat transfer coefficient, heat flux, etc is analyzed numerically.The model built in this paper is suitable for complex working medium of adding phase change microcapsules as well as porous medium composite phase change materials. This work has great significance on the quantitative evaluation of the heat transfer performance, thermal properties measurement and large-scale application of the composite phase change materials have framework structure.